1. Field of the Invention
The instant disclosure relates to a voltage conversion circuit; in particular, to a voltage conversion circuit that can increase conversion efficiency.
2. Description of Related Art
With the electrical technology developed, people require more when using the electric products. In order to provide good products with friendly prices, how to effectively save the volume of the electric product becomes an important topic for the product designers. In the general electric devices, it needs lots of power groups provided as the work voltage, so in order to prevent from using lots of transformers having large volumes to provide power of different voltage values, the Power Converter becomes the most popular power supply device for the product designers.
Please refer to FIG. 1, FIG. 1 shows a circuit diagram of a traditional voltage conversion circuit. The traditional voltage conversion circuit 100 comprises an inductor L′, a N type transistor QN, a P type transistor QP, a voltage controller 110 and an output capacitor COUT′. One terminal of the inductor L′ is connected to the input voltage VIN′. The N type transistor QN has drain connected to another terminal of the inductor L′, has gate receiving the first driving signal LG′ and has source connected to a ground voltage GND′. The P type transistor QP has source connected to drain of the N type transistor QN, has gate connected to the second driving signal UG′ and has drain connected to an output voltage VOUT′. One terminal of the output capacitor COUT′ is connected to drain of the P type transistor QP and another terminal of the output capacitor COUT′ is connected to the ground voltage GND′.
In the prior art, no matter the traditional voltage conversion circuit 100 connects to a light load or a heavy load, the first driving signal LG′ and the second driving signal UG′ have the same driving waveform. Therefore, when the N type transistor QN is switched on or switched off, the P type transistor QP would be correspondingly switched on or switched off. When the first driving signal LG′ is transmitted between a high voltage level and a low voltage level, the N type transistor QN generates a parasitic capacitor Cgs′ and forms a current path. Thus, the traditional voltage conversion circuit 100 would generate a switch current ISWN′ flowing through the parasitic capacitor Cgs′. Likewise, when the second driving signal UG′ is transited between a high voltage level and a low voltage level, the P type transistor QP would generate a parasitic capacitor Cgd′ and forms another current path. Thus, the traditional voltage conversion circuit 100 would generate a switch current ISWP′ flowing through the parasitic capacitor Cgd′. Therefore, the switch currents belong to the currents generated from the inside of the chip, and in the equation of the efficiency transformation, the switch currents ISWN′ and ISWP′ are part of the output current, and thus the conversion efficiency of the traditional voltage conversion circuit 100 would be decreased.